The molecular reactions of the visual process remain to be fully identified within photoreceptors. I have discovered the light-induced phosphorylation of four previously unreported polypeptides in fragmented receptors, prepared from frog retinas. These reactions represent physiological events, as they can be also observed under in vivo conditions. Two of the polypeptides are integral membrane proteins of outer segments and their phosphorylation is graded with cyclic nucleotide levels and with the intensity of light. The observed reactions may participate in the visual process, because external stimuli generally control intracellular events via protein phosphorylation, and because such phosphorylations are usually sensitive to Ca or to cyclic nucleotides, molecules implicated in the visual process. The long-term objective is to study the relevance of the discovered phosphorylations to receptor physiology as they may relate to phototransduction or possible to disc turnover. Specific aims include the characterization of the kinase reactions and identification of the target phosphoproteins. The latter will be tested with existing and newly-raised antibodies. The subcellular location of the protiens will be determined by immunocytochemistry. In addition, the phosphorylations will be studied in "living" retinas, under in vivo conditions, so that the physiological function of the reactions can be further established. The experimental technique will involve standard biochemical procedures. Such studies will contribute to a better understanding of photoreceptor funciton and will also help in learning about the degenerative diseases of the distal retina.